Since I have a Super Magnum laying around with its 8 feet 3 radials, I was rhinhking about replacing the 8 short radials with the longer Super Magnum ones.
what can I expect from it ?
what can I expect from it ?
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Sirio 827 with longer radials
- Thread starter Alexis Mercado
- Start date
You can expect, that antenna will need to be shortened.
Ok. Probably will need to be shortened but
why ? What about performance ?
Penetrator 500 which is a 5/8 wave antenna like the 827, has 105 “ radials. Super Magnum antenna has 108 , is 1/2 wave antenna.
I want to replace the shorter 827 radials because I think this antenna is a 5/8 wave and longer radials should be used since the beginning.
Why Sirio used a bunch of shorter radials instead of longer ones is uncanny for me.
Because longer radials give marginal improvement and are mechanically problematic.
http://www.hamuniverse.com/w5altradialnotes.html
bottom table. It's about 2m antenna but principles are the same.
Mike
http://www.hamuniverse.com/w5altradialnotes.html
bottom table. It's about 2m antenna but principles are the same.
Mike
Alex, I tend to agree with sp5it.
IMO, if you do what you suggest, I think you will have to re-tune the 827, and it may require more than just making the radiator a bit shorter. I think the 827 has a tapped coil and that may need to be adjusted some too.
Why don't your just go for it and then report back what happens?
I would be interested to know what effect the longer radials produce...and if you see 1 - 3 db increase in gain...like some have reported.
IMO, if you do what you suggest, I think you will have to re-tune the 827, and it may require more than just making the radiator a bit shorter. I think the 827 has a tapped coil and that may need to be adjusted some too.
Why don't your just go for it and then report back what happens?
I would be interested to know what effect the longer radials produce...and if you see 1 - 3 db increase in gain...like some have reported.
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Eddy,
The half length radials on the 827 effect vswr more than i thought they would,
we put one up with 4 radials removed to get it past a overhang, i had the idea to check vswr as we added radials, started at 1.5:1 with 4 radials & dropped a little with each radial we added back to needle hardly moving with the 8 radials,
can eight 1/8wave radials equal three or four 1/4wave radials for decoupling the antenna / minimising cmc ?,
probably not but imho if you properly isolate the antenna from the mast & coax you can force the shorter radials to perform more like full size radials,
if anybody sees anything like 3db gain they had TERRIBLE cmc with the short radials.
The half length radials on the 827 effect vswr more than i thought they would,
we put one up with 4 radials removed to get it past a overhang, i had the idea to check vswr as we added radials, started at 1.5:1 with 4 radials & dropped a little with each radial we added back to needle hardly moving with the 8 radials,
can eight 1/8wave radials equal three or four 1/4wave radials for decoupling the antenna / minimising cmc ?,
probably not but imho if you properly isolate the antenna from the mast & coax you can force the shorter radials to perform more like full size radials,
if anybody sees anything like 3db gain they had TERRIBLE cmc with the short radials.
The more you improve the RF ground the shorter the radiating element needs to be for a given frequency.
Performance increases won't really be noticeable to be honest although if you could put a RF current meter on your coax you'd notice a small drop in common mode RFI if you weren't using a choke.
You're right, ideally you should be using four 1/4 wave ones for an elevated antenna and in fact if you look at the new Sirio Tornado 27 it's basically a Sirio 827 but with four almost 1/4 wave long radials. You can use shorter ones if you increase their number, even as short as 1/8 wavelength because it's all about maximising current flow for the the H-plane, or magnetic field, which is at right angles to the E-plane, electrical one, and therefore horizontal on a vertical antenna. Because the maximum current is at the base of the antenna this is where it's the most important to have any radials and as you get further away from the base it becomes less important.
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Yes. The ARRL Antenna Book section on grounding, chapter 3, has 30 odd pages descirbing different options, what's going on and plenty of charts which graph gain vs both radial lengths and the number of radials and it also has graphs showing how the resonant frequency of a fixed length antenna is altered too.
When it comes to something like 4 1/4 wavelength or 8 1/8 wavelength radials performing about the same, and sometimes even better. This is referring to a radial system that is on or just above the earth. In this case this isn't a big deal because the antenna currents on the radials do not electrically end at the ends of the radials, and in fact continues on the earth past the radials.
However, the antenna in question is an elevated antenna that is typically mounted orders of magnitude higher than a "few feet" above the earth. There is no nearby earth in such systems for the currents on said radials to continue past said radials. Because of this, this becomes a different animal entirely. In this case, the radial lengths are electrically more a part of the antenna system, and a change in this setup will have much more of an effect on the antenna's feed point impedance.
I don't think that shortening the vertical element of the antenna alone will be enough to account for this change, very likely an adjustment to the antenna's matching system will be in order as well. I don't know if it will have enough tuning range to account for this change or not.
As mentioned above, this setup will also not be as effective at combating common mode currents, which along with making tuning an antenna easier is the main benefit of having a full length radial system on an elevated antenna so if this becomes an issue you may need to invest in an RF choke.
The dB
However, the antenna in question is an elevated antenna that is typically mounted orders of magnitude higher than a "few feet" above the earth. There is no nearby earth in such systems for the currents on said radials to continue past said radials. Because of this, this becomes a different animal entirely. In this case, the radial lengths are electrically more a part of the antenna system, and a change in this setup will have much more of an effect on the antenna's feed point impedance.
I don't think that shortening the vertical element of the antenna alone will be enough to account for this change, very likely an adjustment to the antenna's matching system will be in order as well. I don't know if it will have enough tuning range to account for this change or not.
As mentioned above, this setup will also not be as effective at combating common mode currents, which along with making tuning an antenna easier is the main benefit of having a full length radial system on an elevated antenna so if this becomes an issue you may need to invest in an RF choke.
The dB
Yes it is. Here is a picture of my working conditions: See pics.
Sirio cover all con band incluidos the si called marines to all the aerials put the beginning of 10 meter band.
What impresa me is the bandwidth of the Gain Master, almost the triple of the 827zsee picture
Alexis, thanks for the drawing of your station. I like the palm tree.
Your GM bandwidth is similar to a GM I had up. It also transmitted a little better. I thought it had a quieter receive than my other vertical CB antennas. Never owned a Sirio 827.
Alexis, I did a model of the 827 below, but I didn't have the dimensions for the matching coil, and other dimensions...so i simulated a good match so I could run the SWR scan for bandwidth. The 827 bandwidth I get is: 1.40:1 MHz at the feed point. Sirio shows 2 MHz which is close to your BW results.
I was surprised with my results for these 827 models. These two models (8 x 55" inch radials vs 4 x 105" inch radials) showed, among other things, I had to increase the length for the radiator about 8" inches...instead of making the radiator shorter, as I stated in my post #6 above.
Models in PDF file below:
Sirio 827GP55''RwMnISOwC 1 36' vs. Sirio 827GP9'RwMnISOwC 2 36'
Your GM bandwidth is similar to a GM I had up. It also transmitted a little better. I thought it had a quieter receive than my other vertical CB antennas. Never owned a Sirio 827.
Alexis, I did a model of the 827 below, but I didn't have the dimensions for the matching coil, and other dimensions...so i simulated a good match so I could run the SWR scan for bandwidth. The 827 bandwidth I get is: 1.40:1 MHz at the feed point. Sirio shows 2 MHz which is close to your BW results.
I was surprised with my results for these 827 models. These two models (8 x 55" inch radials vs 4 x 105" inch radials) showed, among other things, I had to increase the length for the radiator about 8" inches...instead of making the radiator shorter, as I stated in my post #6 above.
Models in PDF file below:
Sirio 827GP55''RwMnISOwC 1 36' vs. Sirio 827GP9'RwMnISOwC 2 36'
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Not the charts I was looking at in the ARRL book. They cover both ground and elevated. I know the OP was talking about elevated, not ground mounted.
You misunderstand. The shortening of the vertical element has to be done as a result of the improved efficiency of the RF ground. And funnily enough in the same section of the ARRL book there's charts galore and a sub-section explaining that too
With all due respect I beg to disagree.
I skimmed through the entire chapter on grounding of the 23'rd edition of the ARRL Antenna Book before posting that post, and I specifically read it before posting this one. The charts of radial length and efficiency (performance) are all for antennas mounted on or near the earth. When they start talking about elevated radial systems, all of that goes away. Said book also talks about elevated antennas only needing 4 1/4 wavelength radials to be as efficient as a large number of radials on a ground mounted antenna.
Typically I agree with most of what you talk about, I find it odd that we would disagree with what is written in the same highly reliable source. I am curious as to what would bring about this difference in perspective.
I understand exactly what you were saying. You were talking about efficiency, I was taking that and factoring in the change in feed point impedance that you will also see when making this change on an elevated antenna, and concluded that the change you would make to account for efficiency will not be enough to account for the change in feed point impedance. To take that a step further, depending on the matching system that antennas uses, adjusting said matching circuit may also not be enough to account for said change.
The DB